This application is a continuation of International Application No. PCT/JP00/07364, filed Oct. 23, 2000, which claims the benefit of Japanese Patent Application No. 11-301675, filed Oct. 22, 1999.
The present invention relates to a belt and an image forming apparatus with the belt, and more particularly relates to a serpentine motion preventing member provided in an inner circumferential surface of an endless belt.
In a conventional image forming apparatus such as an electrophotographic apparatus, an endless belt is used as a belt-shaped like photosensitive member, an intermediate transfer belt, a transfer belt, a paper delivery belt, a fixing belt or the like.
In this case, in general, such an endless belt is supported by two or more rollers and rotationally driven while being subjected to a desired tension. However, since there is slight variation or error in circularity or straightness of the supporting rollers, parallelism of an axis of each roller, or circularity of the endless belt per se or the like, there are cases where the belt would be subjected to a serpentine motion to the right and left. Then, in the case where such an endless belt is used as a transfer belt such as a full color electrophotographic apparatus that needs high precision, the image forming position of each color would be displaced from others upon the color superimposition on the transfer belt, resulting in color misregister due to the serpentine motion of the transfer belt.
Therefore, in order to prevent such a serpentine motion, the serpentine motion preventing member is provided over the full circumferential inner surface of the transfer belt and at the same time, grooves are formed on the rollers around which the transfer belt is laid. The rollers are rotated while the serpentine motion preventing member is retained by the grooves whereby the transfer belt is smoothly traveled without any serpentine motion of the transfer belt, and thus, it is possible to form an excellent image without any color misregister.
However, there are some cases where the serpentine motion preventing member is peeled off from the transfer belt and in an extreme case, a crack would occur in the transfer belt due to a stress caused by the deformation of the serpentine motion preventing member with the rollers or the like.
For this reason, as in, for example, JP-A-08099706, an acrylic foamed material is used as a belt reinforcement base member, and a polyurethane sheet with a limited hardness is adhered thereto to thereby exhibit a stress moderating effect and a serpentine motion preventing effect to the belt.
However, in the case of such a structure, since a large portion of a thickness of the serpentine motion preventing member is occupied by the nonfoamed material, the serpentine motion preventing member is largely deformed at the bent portion of the belt, and the endless belt is subjected to a large stress. Accordingly, in case of use for a long period of time, there is a case that the serpentine motion preventing member would be peeled off.
Then, this phenomenon is remarkable in the case where a diameter of the rollers around which the transfer belt is laid is small and a contact angle of the transfer belt to the rollers is large. Namely, in order to meet the service life of the transfer belt, it is necessary to increase the diameter of the rollers around which the transfer belt is laid and to decrease the contact angle of the transfer belt to the rollers, i.e., to provide the rollers in a multiplicity of axes. This becomes a remarkable obstacle against the miniaturization of the image forming apparatus.
Accordingly, in view of such a current situation, an object of the present invention is to provide a belt having a long service life and an image forming apparatus provided with this belt.
According to the present invention, an endless belt stretched around a plurality of rollers is characterized by having: a serpentine motion preventing member provided on at least one side portion of an inner circumferential surface of the belt body and retained by the rollers, wherein the serpentine motion preventing member is formed of foamed material.
Also, according to the present invention, the serpentine motion preventing member is retained by a retainer groove formed in the rollers.
Also, according to the present invention, the serpentine motion preventing member is retained at a side end of the rollers.
Also, according to the present invention, an average foam diameter of the foamed material is 10 xcexcm or more and 300 xcexcm or less.
Also, according to the present invention, a void rate of the foamed material is 20% or more and 80% or less.
Also, according to the present invention, a surface layer having a void rate that is smaller than that of other portions is formed on at least one of a surface in contact with the rollers and a surface bonded to the belt body of the foamed material.
Also, according to the present invention, the void rate of the surface layer is less than 20%.
Also, according to the present invention, the thickness of the surface layer is 100 xcexcm or less.
Also, according to the present invention, the belt body is a seamless belt.
Also, according to the present invention, an image forming apparatus having an image bearing member and an intermediate transfer belt on which a toner image formed on the image bearing member is to be transferred and wherein the toner image on the intermediate transfer belt is to be transferred to the transfer material, the above-described intermediate transfer belt is any of the belt described above.
Also, according to the present invention, an image forming apparatus having an image bearing member and a transfer delivery belt which bears the transfer material on which a toner image formed on the image bearing member is to be transferred, the above-described transfer belt is any one of the belts described above.
With such an arrangement according to the present invention, the serpentine motion preventing member provided on at least one side portion of an inner circumferential surface of the endless belt body on which the toner image formed on the image bearing member on an outer circumferential surface is transferred and retained by the retainer groove formed in the rollers is formed of foamed material whereby the peel of the serpentine motion preventing member away from the belt body and the damage of the belt body may be prevented.